Honestly I wouldn't worry about anything like that at the moment, just keep doing what you're doing in dark for now. Magna 2 is coming out soon and its possible that that will just fuck up everything we know about the elements.
The big problem with dark right now is regardless of what characters you have it doesn't lend itself well to the new bahamut fights, below that tier with or without zooey dark is still in a strong place, it just falls apart a bit when you hit that point in progression but hey, maybe magna 2 will fix everything. (It won't they have no idea what they're doing)